The present invention relates to an incremental switched deformable mirror (DM) drive which uses analog multiplexers to drive more than one actuator with the same drive amplifier. In practically all known applications of the deformable mirror, the purpose of using the deformable mirror is to provide correction for the phase distortions of the input wavefront, the cause of the input phase distortions being due to one or more of the following (a) atmospherics and other turbulences (b) thermally induced deformations of optical elements (c) gravity effects and (d) static deformations of optical elements. The statistics governing the DM drive requirements are very nearly the same as the spatial and temporal statistics of the input wavefront, since the DM attempts to exactly correct the input wavefront, except that the required DM amplitude is 0.5 times that of the input, due to the doubling of the optical path due to reflection. Except for (a) above, all the others involve very low temporal frequencies, and so at typical sampling frequencies, the incremental drive per sample period is much smaller than the input. What is not obvious, and this is shown below, is the fact that this is true even for the spatial and temporal frequencies involved in the atmospherics.
It is desirable to provide a system applicable to any deformable mirror (DM) drive system, and so is useful in any and all of the adaptive optics systems that use deformable mirrors. To illustrate the need to have such a system applicable to a wide range of requirements, design examples are given for two extreme cases of requirements as follows.
(a) high sampling rate (5 kHz) and high Greenwood frequency (few hundred Hz, depending on strehl error budget allocated to the servo loop), and
(b) low sampling rate (100 Hz) and low equivalent xe2x80x9cGreenwood frequencyxe2x80x9d (few tenths of Hz, such as due to thermal deformations or mirrors).
The sampling rate could be made higher than 5 kHz, depending on system parameters;
The above extreme case requirements are only examples, and should not be taken as an inherent design limit.
In the analysis that follow, use is made of standard formulae that are widely used and accepted as good approximations for the temporal and spatial statistics of the atmospheric phase variations. In particular, the Greenwood frequency is used as a measure of the temporal frequency content of the input, with a few hundred Hz denoting the high end of temporal requirements, and a very low value of a few tenths of a Hz to represent the temporal content of all other effects. In the high frequency cases, the servo bandwidth is derated (multiplied) by a factor of 0.5, in order to account for the fact that the standard formulae do not include the effects of some of the finer details of the servo loop.
Thus, these two extreme cases effectively cover all possible known applications.
All known prior art uses involve one drive amplifier per actuator. There are many examples of this prior art: SAAO, SOR, LAMP, ABL, etc. Such systems are inefficient, as will be shown in the analysis supporting this invention.
Accordingly, it is an object of the present invention to provide an Incremental Switched Deformable Mirror Drive System for a Deformable Mirror (DM) with significantly fewer drive amplifiers without significantly lowering the drive update frequency (bandwidth).
Another object of the invention is to provide an Incremental Switched Deformable Mirror Drive System of the aforementioned type which significantly reduces the volume, weight and power consumption of the drive amplifier electronics, particularly for air-borne and space-based systems.
Yet still a further object of the invention is to provide a system of the aforementioned type which significantly improves hardware reliability by reducing the cabling and number of electrical connections thereto in systems with very large number of actuators and/or high spatial density of actuators, for which conventional one-drive-per-actuator drive system results in almost impossible cabling, connector and power requirements.
Yet still a further object of the invention, is for use in low bandwidth systems allowing for achieving large stroke with relatively low voltage drive.
It is a further object of the invention to accomplish the multiplexing of actuation in a manner which is consistent with the operational requirements of deformable mirror systems in typical applications in both low frequency and high frequency systems, resulting in potential significant savings in power, volume, opening up new design parameters.
A further object of the invention is to provide manufacturing concepts which are introduced for arrangement of deformable mirror actuator arrays, and for high density actuator arrays, leading to distributed two-dimensional actuators.
The invention resides in a method of driving a plurality of actuators comprising the steps of providing a plurality of actuators and a controller having drive output signals for driving said plurality of actuators. At least one multiplexer is provided between said controller and said plurality of actuators and driving said actuators using said controller drive output signals by causing said actuators to be energized and deenergized by mutiplexing through said multiplexer.
Ideally a drive amplifier is provided between said plurality of actuators and said controller and said drive amplifier is used in conjunction with said at least one multiplexer to drive said plurality of actuators.
In one embodiment, a comparator is provided as part of said drive amplifier and is used as a switch, while in another embodiment a plurality of multiplexers is used with the drive amplifier and are configured with said drive amplifier to effect a continuous drive.
Preferably, the plurality of actuators are arranged in an array and are piezoelectric type actuators, and the controller has a limit drive min/max function as well as the controller being provided with a monitoring function which detects and limits differential stroke between actuators.
Ideally said plurality of actuators are located on one side of a board and a plurality of multiplexers are mounted on the other side of said board in a wing like configuration.
The multiplexers may be arranged in a stacked arrangement.